1. Department of Obstetrics and Gynecology Iida Municipal Hospital Iida Japan
2. Department of Obstetrics and Gynecology Nagano Prefectural Kiso Hospital Kiso‐gun Japan
3. Department of Clinical Epidemiology and Health Economics School of Public Health, The University of Tokyo Tokyo Japan
4. Emergency and Critical Care Center Tokyo Metropolitan Hiroo Hospital Tokyo Japan
5. Emergency Life‐Saving Technique Academy of Tokyo Foundation for Ambulance Service Development Tokyo Japan